Demands for enhancing the sense of resource reusing in view of environmental problems are increasing in the industrial world, and movements of recycling resin products have become active. Particularly, it is the case with bumpers of vehicles made of thermoplastic synthetic resin such as polypropylene group resin that a large quantity of defective products that have been deemed to be inappropriate during manufacturing processes and bumpers that have been collected from scrapped cars is brought about, and there are demands for reusing such products.
By the way, the surface of synthetic resin that comprises a bumper of a vehicle is treated with thermosetting resin paint such as polyester urethane. Such a bumper not only exhibits superior heat resistivity or the like but also have a nice appearance with a glossy surface.
However, when products undergo recycling processes with some parts of such paint remaining, paint pieces will be mixed into synthetic resin to hinder its fluidity which might cause reasons of imperfect moldings. Since such paint pieces will come up to the surface, they will spoil the appearance of the bumper even if they are repeatedly painted. Accordingly, a bumper cannot be reused with any paint remaining on the surface of the bumper.
There are accordingly known various methods and devices for removing paint so that they doe not remain on the surface of a bumper. For instance, in the shot blast method, paint is removed through impact of jetted shot or the like. In a method of using a chemical solution such as an ethanol-water mixture, paint is removed by dissolving the same by immersion using this solution.
There is suggested a method for removing paint by generating shear stress between the paint and the resin material by rolling the bumper upon setting a peripheral velocity of a paint side roller to be larger than a peripheral velocity of a non-paint side roller (see Patent Literature 1). More particularly, since the non-paint side roller which rotation is slow will function as a brake that prevents progress of the bumper, the paint is pulled to in a rotating direction through frictional force between this roller and the paint side roller which rotation is fast such that the paint is stripped off from the surface of the resin material.